Take tram No 22 or 25 (in the direction of BÍLÁ HORA or VYPICH) to the "Břevnovský klášter" stop (4 stops from Malovanka stop). The abbey can be seen from the stop.
If you prefer to walk:
You can walk approx. 25 min westwards either along Bělohorská (the street with tram) or Patočkova Streets (main street at the valley bottom, where you can see the monastery all the way), but calm parallel streets may be more suitable. Suggested way is marked in green in the map below.